Which of the following terms describes the force against which the ventricle must expel blood?
A. Afterload
B. Cardiac output
C. Overload
D. Preload
Correct Answer: A. Afterload
Afterload refers to the resistance normally maintained by the aortic and pulmonic valves, the condition and tone of the aorta, and the resistance offered by the systemic and pulmonary arterioles. The afterload of any contracting muscle is defined as the total force that opposes sarcomere shortening minus the stretching force that existed before contraction. Applying this definition to the heart, afterload can be most easily described as the “load” against which the heart ejects blood.
Option B: Cardiac output is the amount of blood expelled from the heart per minute. Cardiac output (CO) is the amount of blood pumped by the heart minute and is the mechanism whereby blood flows around the body, especially providing blood flow to the brain and other vital organs. The body’s demand for oxygen changes, such as during exercise, and the cardiac output is altered by modulating both heart rate (HR) and stroke volume (SV).
Option C: Overload refers to an abundance of circulating volume. Hypervolemia occurs when blood volume is increased and can occur through renal failure, congestive heart failure, liver failure, excessive sodium intake, or any other dysfunction of sodium regulation. Furthermore, prolonged hypertension may result in renal damage eventually culminating in fluid imbalance.
Option D: Preload is the volume of blood in the ventricle at the end of the diastole. Also termed left ventricular end-diastolic pressure (LVEDP), preload is a measure of the degree of the ventricular stretch when the heart is at the end of diastole. Preload, in addition to afterload and contractility, is one of the three main factors that directly influence stroke volume (SV), the amount of blood pumped out of the heart in one cardiac cycle.
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